1,174 research outputs found
Efficient photon counting and single-photon generation using resonant nonlinear optics
The behavior of an atomic double lambda system in the presence of a strong
off-resonant classical field and a few-photon resonant quantum field is
examined. It is shown that the system possesses properties that allow a
single-photon state to be distilled from a multi-photon input wave packet. In
addition, the system is also capable of functioning as an efficient
photodetector discriminating between one- and two-photon wave packets with
arbitrarily high efficiency.Comment: 4 pages, 2 figure
Bioinspired Asymmetric-Anisotropic (Directional) Fog Harvesting Based on the Arid Climate Plant Eremopyrum orientale
Asymmetric-anisotropic (directional) fog collection behaviour is observed for leaves of the arid climate plant species Eremopyrum orientale. This is underpinned by a hierarchical surface structure comprising macroscale grooves, microscale tilted cones (in the direction of water flow), and nanoscale platelets. Soft lithography combined with either nanocoating deposition or functional nanoimprinting has been used to replicate this highly-efficient directional water collection mechanism
Berry's Phase in the Presence of a Dissipative Medium
We consider the spin 1/2 model coupled to a slowly varying magnetic field in
the presence of a weak damping represented by a Lindblad-form operators. We
show that Berry's geometrical phase remains unaltered by the two dissipation
mechanism considered. Dissipation effects are twofold: a shrinking in the
modulus of the Bloch's vector, which characterizes coherence loss and a time
dependent (dissipation related) precession angle. We show that the line
broadening of the Fourier transformation of the components of magnetization is
only due to the presence of dissipation.Comment: 19 pages, 2 figure
Full quantum solutions to the resonant four-wave mixing of two single-photon wave packets
We analyze both analytically and numerically the resonant four-wave mixing of
two co-propagating single-photon wave packets. We present analytic expressions
for the two-photon wave function and show that soliton-type quantum solutions
exist which display a shape-preserving oscillatory exchange of excitations
between the modes. Potential applications including quantum information
processing are discussed.Comment: 7 pages, 3 figure
Adiabatic Approximation in the Density Matrix Approach: Non-Degenerate Systems
We study the adiabatic limit in the density matrix approach for a quantum
system coupled to a weakly dissipative medium. The energy spectrum of the
quantum model is supposed to be non-degenerate. In the absence of dissipation,
the geometric phases for periodic Hamiltonians obtained previously by M.V.
Berry are recovered in the present approach. We determine the necessary
condition satisfied by the coefficients of the linear expansion of the
non-unitary part of the Liouvillian in order to the imaginary phases acquired
by the elements of the density matrix, due to dissipative effects, be
geometric. The results derived are model-independent. We apply them to spin 1/2
model coupled to reservoir at thermodynamic equilibrium.Comment: 24 pages (new version), accepted for publication in Physica
The Magnetic Casimir Effect
The Casimir effect results from alterations of the zero-point electromagnetic
energy introduced by boundary-conditions. For ferromagnetic layers separated by
vacuum (or a dielectric) such boundary-conditions are influenced by the
magneto-optical Kerr effect. We will show that this gives rise to a long-range
magnetic interaction and discuss the effect for two different configurations
(magnetization parallel and perpendicular to the layers). Analytical
expressions are derived for two models and compared to numerical calculations.
Numerical calculations of the effect for Fe are also presented and the
possibility of an experimental observation of the Casimir magnetic interaction
is discussed
A review on anticipatory grief and lessons learnt from the history of Abu Bakr r.a.
Grief is defined as ‘the internal experience of a person to the loss of something loved and valued’. It is a normal and expected reaction to loss. While anticipatory grief is defined as ‘an emotional response that is experienced before a true loss’, a concept focusing on that a person might experience grief when the loss of a close loved one was anticipated, but had not yet occurred. The history of Abu Bakr r.a. was reviewed especially from the period of a few months before and recently after the death of the prophet s.a.w. It was noted that he appeared strong while others were down grieving upon the news of the prophet s.a.w.’s death. It was also noted that Abu Bakr r.a. has been grieving when he anticipated that the prophet was going to die. Literatures on anticipatory grief were reviewed. Evidence are conflicting on the role of anticipatory grief. Factors that lead to these differences will be reviewed. The protective factors in Abu Bakr r.a. that helped maintain his composure after the death of prophet Muhammad s.a.w. and later led him to be pledged as the first caliph of the Muslim nation will be discussed
Theoretical analysis of neutron scattering results for quasi-two dimensional ferromagnets
A theoretical study has been carried out to analyse the available results
from the inelastic neutron scattering experiment performed on a quasi-two
dimensional spin-1/2 ferromagnetic material . Our formalism is based
on a conventional semi-classical like treatment involving a model of an ideal
gas of vortices/anti-vortices corresponding to an anisotropic XY Heisenberg
ferromagnet on a square lattice. The results for dynamical structure functions
for our model corresponding to spin-1/2, show occurrence of negative values in
a large range of energy transfer even encompassing the experimental range, when
convoluted with a realistic spectral window function. This result indicates
failure of the conventional theoretical framework to be applicable to the
experimental situation corresponding to low spin systems. A full quantum
formalism seems essential for treating such systems.Comment: 16 pages, 6 figures, 1 Table Submitted for publicatio
Classical heisenberg antiferromagnet away from the pyrochlore lattice limit: entropic versus energetic selection
The stability of the disordered ground state of the classical Heisenberg
pyrochlore antiferromagnet is studied within extensive Monte Carlo simulations
by introducing an additional exchange interaction that interpolates
between the pyrochlore lattice () and the face-centered cubic lattice
(). It is found that for as low as , the system is
long range ordered : the disordered ground state of the pyrochlore
antiferromagnet is unstable when introducing very small deviations from the
pure limit. Furthermore, it is found that the selected phase is a
collinear state energetically greater than the incommensurate phase suggested
by a mean field analysis. To our knowledge this is the first example where
entropic selection prevails over the energetic one.Comment: 5 (two-column revtex4) pages, 1 table, 7 ps/eps figures. Submitted to
Phys. Rev.
Current Distribution in the Three-Dimensional Random Resistor Network at the Percolation Threshold
We study the multifractal properties of the current distribution of the
three-dimensional random resistor network at the percolation threshold. For
lattices ranging in size from to we measure the second, fourth and
sixth moments of the current distribution, finding {\it e.g.\/} that
where is the conductivity exponent and is the
correlation length exponent.Comment: 10 pages, latex, 8 figures in separate uuencoded fil
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